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[online-glom:gwt-glom.git] / src / main / java / org / glom / web / server / database / ListDBAccess.java

/*
 * Copyright (C) 2011 Openismus GmbH
 *
 * This file is part of GWT-Glom.
 *
 * GWT-Glom is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * GWT-Glom is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with GWT-Glom.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.glom.web.server.database;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

import org.glom.libglom.Document;
import org.glom.libglom.Field;
import org.glom.libglom.LayoutFieldVector;
import org.glom.libglom.LayoutItem_Field;
import org.glom.libglom.SortClause;
import org.glom.libglom.SortFieldPair;
import org.glom.web.server.Log;
import org.glom.web.server.Utils;
import org.glom.web.shared.DataItem;

import com.mchange.v2.c3p0.ComboPooledDataSource;

/**
 *
 */
public abstract class ListDBAccess extends DBAccess {
        protected LayoutFieldVector fieldsToGet;

        protected ListDBAccess(Document document, String documentID, ComboPooledDataSource cpds, String tableName) {
                super(document, documentID, cpds, tableName);
        }

        protected abstract String getSelectQuery(SortClause sortClause);

        protected abstract String getCountQuery();

        protected ArrayList<DataItem[]> getListData(int start, int length, boolean useSortClause, int sortColumnIndex,
                        boolean isAscending) {

                // create a sort clause for the column we've been asked to sort
                SortClause sortClause = new SortClause();
                if (useSortClause) {
                        org.glom.libglom.LayoutItem item = fieldsToGet.get(sortColumnIndex);
                        LayoutItem_Field layoutItemField = LayoutItem_Field.cast_dynamic(item);
                        if (layoutItemField != null)
                                sortClause.addLast(new SortFieldPair(layoutItemField, isAscending));
                        else {
                                Log.error(documentID, tableName, "Error getting LayoutItem_Field for column index " + sortColumnIndex
                                                + ". Cannot create a sort clause for this column.");
                        }
                } else {
                        // create a sort clause for the primary key if we're not asked to sort a specific column
                        int numItems = Utils.safeLongToInt(fieldsToGet.size());
                        for (int i = 0; i < numItems; i++) {
                                LayoutItem_Field layoutItem = fieldsToGet.get(i);
                                Field details = layoutItem.get_full_field_details();
                                if (details != null && details.get_primary_key()) {
                                        sortClause.addLast(new SortFieldPair(layoutItem, true)); // ascending
                                        break;
                                }
                        }
                }

                ArrayList<DataItem[]> rowsList = new ArrayList<DataItem[]>();
                Connection conn = null;
                Statement st = null;
                ResultSet rs = null;
                try {
                        // Setup the JDBC driver and get the query. Special care needs to be take to ensure that the results will be
                        // based on a cursor so that large amounts of memory are not consumed when the query retrieve a large amount
                        // of data. Here's the relevant PostgreSQL documentation:
                        // http://jdbc.postgresql.org/documentation/83/query.html#query-with-cursor
                        conn = cpds.getConnection();
                        conn.setAutoCommit(false);
                        st = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
                        st.setFetchSize(length);
                        String query = getSelectQuery(sortClause) + " OFFSET " + start;
                        // TODO Test memory usage before and after we execute the query that would result in a large ResultSet.
                        // We need to ensure that the JDBC driver is in fact returning a cursor based result set that has a low
                        // memory footprint. Check the difference between this value before and after the query:
                        // Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()
                        // Test the execution time at the same time (see the todo item in getLayoutListTable()).
                        rs = st.executeQuery(query);

                        // get the results from the ResultSet
                        rowsList = convertResultSetToDTO(length, fieldsToGet, rs);
                } catch (SQLException e) {
                        Log.error(documentID, tableName, "Error executing database query.", e);
                        // TODO: somehow notify user of problem
                } finally {
                        // cleanup everything that has been used
                        try {
                                if (rs != null)
                                        rs.close();
                                if (st != null)
                                        st.close();
                                if (conn != null)
                                        conn.close();
                        } catch (Exception e) {
                                Log.error(documentID, tableName,
                                                "Error closing database resources. Subsequent database queries may not work.", e);
                        }
                }
                return rowsList;
        }

        /*
         * Get the number of rows a query with the table name and layout fields would return. This is needed for the /* list
         * view pager.
         */
        protected int getResultSizeOfSQLQuery() {

                Connection conn = null;
                Statement st = null;
                ResultSet rs = null;
                try {
                        // Setup and execute the count query. Special care needs to be take to ensure that the results will be based
                        // on a cursor so that large amounts of memory are not consumed when the query retrieve a large amount of
                        // data. Here's the relevant PostgreSQL documentation:
                        // http://jdbc.postgresql.org/documentation/83/query.html#query-with-cursor
                        conn = cpds.getConnection();
                        conn.setAutoCommit(false);
                        st = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
                        String query = getCountQuery();
                        // TODO Test execution time of this query with when the number of rows in the table is large (say >
                        // 1,000,000). Test memory usage at the same time (see the todo item in getTableData()).
                        rs = st.executeQuery(query);

                        // get the number of rows in the query
                        rs.next();
                        return rs.getInt(1);

                } catch (SQLException e) {
                        Log.error(documentID, tableName, "Error calculating number of rows in the query.", e);
                        return -1;
                } finally {
                        // cleanup everything that has been used
                        try {
                                if (rs != null)
                                        rs.close();
                                if (st != null)
                                        st.close();
                                if (conn != null)
                                        conn.close();
                        } catch (Exception e) {
                                Log.error(documentID, tableName,
                                                "Error closing database resources. Subsequent database queries may not work.", e);
                        }
                }
        }

}